Toward closure between predicted and observed particle viscosity over a wide range temperature and relative humidity

Abstract

Abstract. Atmospheric aerosols can exist in amorphous semi-solid or glassy phase states whose viscosity varies with atmospheric temperature and relative humidity. The temperature and humidity dependence of viscosity has been hypothesized to be predictable from the combination of a water-organic binary mixing rule of the glass transition temperature, a glass transition temperature scaled viscosity fragility parameterization, and a water uptake parameterization. This work presents a closure study between predicted and observed viscosity for sucrose and citric acid. Viscosity and glass transition temperature as a function of water content are compiled from literature data and used to constrain the fragility parameterization. New measurements characterizing viscosity of sub-100 nm particles using the dimer relaxation method are presented. These measurements extend the available data of temperature and humidity dependent viscosity to −28 ºC. Predicted relationships agree well with observations at room temperature and with measured isopleths of constant viscosity at ~107 Pa s and warmer than −28 ºC. Discrepancies at colder temperatures are observed for sucrose particle. Simulations with the kinetic multi-layer model of gas-particle interactions suggest that the observed deviations at colder temperature for sucrose can be attributed to kinetic limitations associated with water uptake at the timescales of the dimer relaxation experiments. Using the available information, updated equilibrium phase-state diagrams (−80 ºC

Humidity-Dependent Viscosity of Secondary Organic Aerosol from Ozonolysis of β-Caryophyllene: Measurements, Predictions, and Implications

“…D f , which characterizes the deviation of the temperature dependence of viscosity from an Arrhenius behavior, , was assumed to be 10 based on our previous study . The value of D f is assumed to be independent of RH. ,,, This assumption is consistent with previous studies that found that the value of D f in sucrose and citric acid is independent of water content, except for anhydrous sucrose. ,, …”

“…54,55,101,102 This assumption is consistent with previous studies that found that the value of D f in sucrose and citric acid is independent of water content, except for anhydrous sucrose. 99,103,104 2.5. Prediction of Viscosity Using a Mole-Fraction Based Arrhenius Mixing Rule.…”

Direct observation and assessment of phase states of ambient and lab-generated sub-micron particles upon humidification

“…30 However, these techniques are limited to large particles or aerosol material masses and could not be extended to the sub-micron size range. Viscosity and phase state of nanoparticles has been assessed based on dimer coalescence, [31][32][33][34][35] but this technique is limited by narrow accessible viscosity range (10 5 -10 8 Pa s). Moreover, these techniques mentioned above are mainly designed based on surrogates of ambient particles, making it a challenge to apply them in the direct measurements of ambient aerosol particles viscosity.…”